CVE-2022-20692: Cisco IOS XE NETCONF DoS Vulnerability

CVE-2022-20692 Overview

A vulnerability in the NETCONF over SSH feature of Cisco IOS XE Software could allow a low-privileged, authenticated, remote attacker to cause a denial of service condition (DoS) on an affected device. This vulnerability is due to insufficient resource management when handling NETCONF over SSH connections. An attacker could exploit this vulnerability by initiating a large number of NETCONF over SSH connections, ultimately exhausting device resources and causing the device to reload.

Critical Impact

Successful exploitation allows an authenticated attacker to cause affected Cisco IOS XE devices to reload, resulting in service disruption across network infrastructure relying on these devices for routing, switching, or other critical network functions.

Affected Products

• Cisco IOS XE versions 3.15.1xbs through 3.15.2xbs
• Cisco IOS XE versions 16.3.1 through 16.12.6a
• Cisco IOS XE versions 17.1.1 through 17.2.3

Discovery Timeline

• April 15, 2022 - CVE-2022-20692 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20692

Vulnerability Analysis

This vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption), which occurs when the NETCONF over SSH subsystem in Cisco IOS XE fails to properly manage and limit resource allocation for incoming connections. The NETCONF protocol provides a mechanism to install, manipulate, and delete the configuration of network devices over SSH transport. When the device does not adequately enforce connection limits or resource boundaries, an authenticated attacker can establish numerous concurrent NETCONF sessions that consume critical system resources such as memory and process handles.

The attack requires low-privilege authentication, meaning the attacker must have valid credentials to establish SSH connections to the device. However, once authenticated, there are insufficient controls to prevent resource exhaustion through connection flooding. This represents a failure in the resource management logic within the NETCONF subsystem that should normally enforce limits on concurrent sessions per user or per source.

Root Cause

The root cause stems from insufficient resource management within the NETCONF over SSH feature implementation. The vulnerability exists because the software does not properly enforce limits on the number of concurrent NETCONF sessions or fails to implement adequate resource quotas for authenticated users. This allows connection resources to be exhausted when an attacker opens numerous simultaneous NETCONF over SSH sessions, eventually depleting available system resources and triggering a device reload.

Attack Vector

The attack is network-based and requires low-privileged authenticated access to the target device's SSH service. An attacker would need to:

1. Obtain valid credentials for the Cisco IOS XE device (even low-privilege accounts are sufficient)
2. Initiate multiple NETCONF over SSH connections to the device
3. Maintain these connections open to exhaust system resources
4. Continue opening new connections until resource limits are reached, causing the device to reload

The attack does not require user interaction and can be automated once valid credentials are obtained. Since the attacker only needs low-privilege access, compromised accounts with minimal permissions can still be leveraged to execute this denial of service attack.

Detection Methods for CVE-2022-20692

Indicators of Compromise

• Unusual spike in the number of concurrent SSH sessions on affected Cisco IOS XE devices
• Multiple NETCONF over SSH connections originating from the same source IP address or user account
• Device memory utilization increasing abnormally without corresponding legitimate activity
• Unexpected device reloads or crash logs indicating resource exhaustion

Detection Strategies

• Monitor SSH connection logs for abnormal patterns such as rapid connection attempts from single sources
• Implement network-based detection rules to identify high volumes of SSH traffic to management interfaces on Cisco devices
• Configure SNMP traps or syslog alerts for memory threshold violations on IOS XE devices
• Use SentinelOne Singularity to monitor network traffic patterns and identify anomalous connection behavior to network infrastructure

Monitoring Recommendations

• Enable accounting logs for SSH and NETCONF sessions to track connection patterns and user activity
• Set up baseline metrics for normal NETCONF session counts and alert when thresholds are exceeded
• Implement centralized logging with SIEM integration to correlate connection events across multiple network devices
• Deploy continuous monitoring of device health metrics including memory and CPU utilization

How to Mitigate CVE-2022-20692

Immediate Actions Required

• Apply the security patches referenced in the Cisco Security Advisory
• Review and audit all user accounts with SSH access to affected devices, removing unnecessary access
• Implement network access control lists (ACLs) to restrict SSH and NETCONF access to authorized management networks only
• Consider temporarily disabling the NETCONF feature if not required for operations until patching is complete

Patch Information

Cisco has released software updates that address this vulnerability. Administrators should consult the Cisco Security Advisory to determine the appropriate fixed software release for their specific IOS XE version. The advisory contains detailed information about affected versions and the corresponding patched releases.

Workarounds

• Restrict SSH and NETCONF access to the device by implementing infrastructure ACLs that permit connections only from trusted management networks
• If NETCONF is not required for device management, disable the feature using no netconf-yang command in global configuration mode
• Implement rate limiting on SSH connections at network boundaries to reduce the speed at which an attacker could exhaust resources
• Use strong authentication mechanisms and monitor for credential compromise to limit attacker access

# Disable NETCONF-YANG if not required
configure terminal
no netconf-yang
end
write memory

# Restrict SSH access to management network
configure terminal
ip access-list extended SSH-RESTRICT
 permit tcp 10.0.0.0 0.0.0.255 any eq 22
 deny tcp any any eq 22
exit
line vty 0 15
 access-class SSH-RESTRICT in
end
write memory